1. Field of the Invention
The present invention relates to disk drives for computer systems. More particularly, the present invention relates to a disk drive comprising a cover having slots near a shaft aperture for reducing resonance.
2. Description of the Prior Art
A computer system usually includes one or more disk drives for economical, non-volatile data storage. FIG. 1 shows a prior art disk drive 100 disclosed, for example, in U.S. Pat. No. 5,282,100 to Tacklind et al. which includes a housing formed by fitting a cover comprising an inner layer 102 and an outer layer 104 to a base 106 to create a sealed head disk assembly (HDA) chamber. The HDA includes one or more disks 108 stacked in a spaced-apart relationship on a spindle motor hub and rotated by a spindle motor (not shown). The disks 108 rotate in close proximity to a head 114 that is disposed by means of a head gimbal assembly (HGA) attached to one of a plurality of actuator arms 110.
The spindle motor includes a stationary element such as a fixed spindle shaft 116 affixed to the disk drive housing at the base and cover to define and stabilize a spindle axis about which a hub rotates the disks 108. A stator of the spindle motor, as well as bearings and seals, are secured between the fixed spindle shaft 116 and the rotating hub. To create this stabilized spindle axis, inner layer 102 includes shaft aperture 118 for receiving a fastener, such as a screw 120, for rigidly attaching the inner layer 102 to the fixed spindle shaft 116.
The actuator arms 110 are part of a head stack assembly (HSA) which is rotated about a pivot bearing assembly by a voice coil motor (VCM) 112. The pivot bearing assembly includes a stationary element such as a pivot shaft 122 that is fixed to the disk drive housing at the base 106 and inner layer 102 of the cover to define and stabilize a pivot axis for the HSA. Typically, the pivot shaft 122 is rigidly coupled to the cover (e.g., by screw 124) and to the base 106. The rigid attachment of the spindle and pivot shafts fixes and stabilizes the relationship of the spindle axis and the pivot axis to control head positioning error. As the spindle motor rotates, the bearings and the fixed spindle shaft 116 tend to vibrate at a first set of characteristic frequencies associated with the bearings. The spindle motor and disk pack also tend to vibrate creating a resonance at a second set of frequencies associated with forward and reverse pitch modes of the spindle motor. If the first set frequencies line up with the second set of frequencies (vibration modes), the resulting resonance can perturb the actuator arms 110 impairing the ability of the disk drive 100 to maintain the heads 114 over the centerline of data tracks during read and write operations. If the heads 114 move off track, the fidelity of data written to and read from the disks 108 degrades and may result in failures. Thus, it is desirable to prevent vibration frequencies characteristic of the bearings and fixed spindle shaft 116 from lining up with vibration modes characteristic of the spindle motor and disk pack.
FIG. 2 shows a cover of a prior art HDA intended to reduce the resonances by shifting vibration frequencies characteristic of the fixed spindle shaft 116 away from the vibration frequencies characteristic of the spindle motor bearings. A washer 126 is attached to the inner layer 102 of the cover using a visco damping adhesive (the cover of FIG. 2 is inverted). The washer 120 is aligned concentric with the shaft aperture 118 and abuts the fixed spindle shaft 116 creating a damping effect. The damping effect of the washer 126 shifts the vibration mode frequencies characteristic of the motor and disk pack away from the vibration frequencies characteristic of the spindle motor bearings. However, incorporating the washer 126 requires an additional component in the disk drive 100, and requires an additional manufacturing step. Further, the visco damping adhesive for attaching the washer 126 to the inner layer 102 of the cover may creep and become less secure with time and temperature.
There is, therefore, a need to reduce resonances in a disk drive in a secure, cost-effective manner.
The present invention may be regarded as a disk drive with reduced resonance, comprising a disk, a fixed spindle shaft disposed axially through the disk, a spindle motor for rotating the disk about the fixed spindle shaft, wherein a resonance is associated with the spindle motor rotating the disk. The disk drive further comprises a head, an actuator arm for actuating the head radially over the disk, a base, and a cover attached to the base to form a head disk assembly chamber. The cover comprises a shaft aperture positioned over the fixed spindle shaft, the shaft aperture for receiving a fastener for attaching the cover to the fixed spindle shaft. The cover further comprises a plurality of slots proximate the shaft aperture, wherein the shaft aperture and slots provide a flexible support for the fixed spindle shaft which reduces the resonance associated with the spindle motor.
In one embodiment, the slots comprise a plurality of slot apertures. In another embodiment, the slots comprise a plurality of grooves. In yet another embodiment, the cover comprises an inner and outer layer, and the inner layer comprises the slots. In yet another embodiment, the slots comprise at least one spoke extending substantially radially from the shaft aperture. In yet another embodiment, the slots comprise at least one arc substantially concentric with the shaft aperture. In yet another embodiment, the slots comprise at least one spoke extending substantially radially from the shaft aperture, and at least one arc substantially concentric with the shaft aperture.
The present invention may also be regarded as a method for manufacturing a disk drive with reduced resonance. A shaft aperture is formed in a cover, and plurality of slots are formed in the cover proximate the shaft aperture. A head disk assembly is disposed into a base of a head disk assembly chamber. The head disk assembly comprises a disk, a fixed spindle shaft, and a motor for rotating the disk about the fixed spindle shaft. The cover is attached to the base of the head disk assembly chamber by attaching a fastener to the fixed spindle shaft through the shaft aperture. The slots provide a flexibility in the cover which reduces a resonance associated with the spindle motor rotating the disk.